A family of five recently replaced its 5-gallon-per-minute shower heads with water-saving 2-gallon-per-minute shower heads. Each member of the family averages 8 minutes in the shower per day. In a 30-day period, how many fewer gallons of water will the family use with the new shower heads?
a. 60.
b. 800.
c. 2400.
d. 3600.
e. 7200.